Polypeptides have been widely used in the field of medicine and pharmaceutics such as in the development of anti-tumor drugs, cardiovascular drugs, vaccines, anti-virus drugs, diagnostic kits and the like (Leader et. al, 2008). However, the production of polypeptides remains a bottleneck for the rapidly increasing market requirements. Solid-phase chemical synthesis is a conventional method for polypeptide production. However, if the polypeptide to be produced has more than 30 amino acids, the cost and difficulty for synthesis increase significantly (Bray et al., 2003).
Another efficient strategy is to produce polypeptides recombinantly in a host cell, such as Escherichia coli (E. coli). E. coli expression system has many advantages, such as fast-growing, high expression level and low costs for production. By using the E. coli system, one can conveniently obtain desired target polypeptides by introducing an exogenous gene which can be further manipulated to introduce modifications in the encoded amino acid sequence. This method is convenient and easy to scale up. More than 30% of the recombinant therapeutic polypeptides currently available on the market are produced using E. coli (Kamionka et. al, 2011; Demain et. al, 2009; Walsh, 2003 and 2006). However, polypeptides less than 100 amino acids in length tend to be degraded by endogenous proteases, which results in a significant reduction in the yields (Murby et. al, 1996; Kuliopulo et. al, 1994; Hannig t. al, 1998).
Protein purification is a key step for the recombinant peptide production methods. It is reported that the cost for isolation and purification covers about 60-80% of the total cost for the production of recombinant polypeptides (Chen Hao et. al, 2002). The conventional methods for purification of recombinant polypeptides include ion exchange chromatography, hydrophobic interaction chromatography, affinity chromatography, and the like. Ion exchange chromatography and hydrophobic interaction chromatography have some special requirements for the starting samples, which largely limits their use. The affinity chromatography may typically result in a high yield of up to 90%, which makes it the most popular method for purification of recombinant proteins. Conventional affinity chromatography techniques involve the fusion expression with a His-tag or a Glutathione transferase tag (GST-tag), which provides a universal means for production of various target polypeptides. However, the affinity columns are expensive and thus limit the applications of affinity chromatography techniques in the industry.
There is still a need of cost-efficient and convenient methods for production and purification of polypeptides.